This invention relates to current limiting circuits, and more particularly to such circuits for use in AC power lines.
Circuits are known for use in AC power systems which are tuned to series resonance at the AC power frequency, and which are detuned in response to a fault current on the AC power line to afford a high impedance in the line and subsequent current limiting. A number of such circuits are shown in U.S. Pat. No. 3,418,532, issued to Becker. In FIG. 2 of the Becker patent a pair of series resonant inductive-capacitive circuit legs are shown connected in parallel, having a cross leg between the circuit nodes connecting the inductors and capacitors in each of the parallel legs. The cross leg contains a saturable choke X.sub.S in series with a resistor R. In normal operation the saturable choke presents a high impedance between the nodes, and the series resonant legs present substantially no resistance to the flow of current. When a fault current creates a voltage across the saturable choke, the choke is driven into saturation rendering it highly conductive and detuning the series inductive capacitive legs. Subsequent current flow through the circuit, when detuned, is limited by the resistance R to a safe value. Oscillation prevention is also provided by resistance R. However, the Becker disclosure, as well as all other known references, allows the voltage across the capacitors to increase momentarily to a very high level when the saturable choke assumes a conductive condition upon the occurrence of a fault. Building capacitors to withstand this momentary high voltage is quite costly, and renders any resulting circuit module very bulky. A short circuit limiting network having small volume is desirable which provides fault current protection in an AC power system, and at the same time provides protection for the network itself.